Cross-field generator



l the welding industry,

Patented Dec. 26, 1939 William B. Harding,

Pittsburgh, Pa., assignor to Westinghouse Electric & ManufacturingCompany, East Pittsburgh, Pa., a corporation of Pennsylvania,

Application November 2v, 1937, serai No. 176,862

5 Claims.

to generators, direct current My invention relates, generally, and ithas particular reference to generators of the cross-field type.

'I'hrough recent developments, generators of the cross-field type havecome into wide vuse in particularly because of their flexibility ofoperation and substantially constant current characteristics. Sincegenera-v tors of this type rely mainly upon'series-eld windings for theproduction of the magnetic flux therein, their open circuit voltage,which-must accordingly be generated by the residual magnetism of thefield pole members, is substantially lower than that of. generators ofother types. It is, therefore, not uncommon, when the electrode of awelding generator of the cross-eld type comes into contact with theelectrode of a generator having a higher open circuit voltage, to havethe residual polarity of the cross-field generator reversed, because ofthe circulating current which is forced through its series-field windingin the reverse direction by contact with the electrode of the highervoltage machine. Since it is essential in arc-welding to maintain thedesired polarity of the welding electrode in order to .securesatisfactory welds, further developments have been found necessary inconnection with generators 'of' the cross-field type, to ensure theterminal polarityof the generator being reestablished or maintained,even after an accidental reversal-of the residual magnetism of thegenerator. In general, polarity'determining control systems forcross-field generators have utilized an external source in connectionwith a field winding of the generator for providing auxiliary excitationthereof,- in order to fix the polarity of the residual magnetism ofthefield pole member and definitely determine the terminal polarity of thegenerator. Such'systems, while performing ef- 'fectively to minalpolarity of the generator, have, by increasingthe iluxthrough the fieldpole member, necessarily increased the circulating armature currentinduced thereby in the auxiliary brush circuit. In some instances,the-increase of the circulating current in the auxiliary brush circuit'has-been of such extentvas to cause .undesirable sparking of thebrushes when the generatoris running withoutload, and-adversely'aiectthestability of operation of the generatorwhen runl ning under load.

Itis, therefore, generally an object of my invention to improve thecommutation and stability fcfa generator of the field type havingauxil-v iaryileld pole excitation.

both control and determine the ter More specifically, it is an object ofmy inven- -t'ion to utilize a dierential in air gap reluctance in agenerator of the cross-field type for preventing auxiliaryY excitationof a eld pole winding from causing an increase in the no-load armaturecirculating current. j

Another object of .my invention is to provide uneven air gaps in agenerator'of the cross-field type having auxiliary polarity control eldpole excitation for preventing an increase in the noload magnetomotiveforce acting on a field pole member from increasing the effective airgap flux of the generator.

Still another object of my invention is to increase the air gap spacingin the direction of armature rotation, in a generatorof the cross-fieldtype having auxiliary polarity control field pole excitation' fordecreasing the auxiliary brush armature current and improving thecommutation and stability of the generator.

Other objects of the invention will, in part, be obvious, and, in part,appear hereinafter.

For a more complete understanding of the nature and scope of myinvention, reference may b e had to the following in connection with theaccompanying drawing, in which: l

Figure 1 represents diagrammatically a preferred' embodiment'of myinvention in connection with a generator of the cross-field type; and,Fig. 2 illustrates an alternative form of my' invention as lpracticedwith a generator of. the cross-field type.

Referring to Fig. l, the reference numeral I0 may denote generally agenerator of the crossfleld type comprising, a frame II, an armature I2,and field pole members I3 and I5 having series field windings I'l and I9and commutating field windings 2l and 23, respectively, positionedthereon.- An .external source of auxiliary excitation 20 maybe connectedwith the series eld windings I'I vand I9 and the commutating eldwindings 2I and'23 of the 'generator for determining and controlling theterminal polarity thereof. A reversingswitch 24 may be .interposedbetween the sourceand the windings so that the polarity of the residualmagnetism of the field p ole members may be;l altered at will forreversing the-terminal polarity of the generator. a

In a preferred embodimentoffmy invention,

the shoe portions 2s and 21, ofthe -neld po1edetailed description,takenl members I3 and I5, respectively, may be disposed tion of thearmature I2, which in this case is counter-clockwise, as indicated bythe curved arrow.

Referring more particularly to Fig. 1 it may 5 be seen that generator I0is generally of the cross-field type, as disclosed in the pendingapplication of John I-I. Blankenbuehler, Serial No. 26,871, assigned tothe assignee of this application, and comprises a frame II, which fieldpole members I3 and I5 positioned therein, comprising main body portions3| and 33, respectively, about which are disposed series field windingsI1 and I9, `and. enlarged shoe portions 25 and 21, adjacent to thearmature. These shoe portions may be so disposed in relation to thearmature I2 that the air gaps 29 and 30 which separate the shoe portions25 and 21 therefrom, may, as shown, be of gradually increasing lengthradially, in the direction of armature rotation.

vThe armature I2 may, as herein shown, be provided with main brushes 34and auxiliary brushes 35,'in the usual manner of cross-field generators.The main brushes are disposed in `connection with the series-fieldlwindings I1 and I3 and the commutating field windings 2I and 2-3, forconnection to a load circuit, which comprises an electrode 36 and work31. 'I'he auxiliary brushes are normally connected together by aconductor 33, to provide a path for 30 an armature circulating currentwhich is induced therein when the armature conductors cut the residualflux of the iield pole members, indicated by the dotted line 4 -I. Thiscirculating armature current in turn produces a cross- 35 field magneticiiux which .traverses the shoe portions 25 and 21, respectively, andalso a portion of the armature as shown by the dotted line -2, andinduces a voltage between the main brushes 34.

40 As shown in this instance, the auxiliary ex-` citationI source 20may, comprise a transformer 40, having a core member 4I with a primarywinding 42 thereon, adapted to beenergized from an alternating currentsource, and a secondary 45 winding 43 disposed in connection with arectifier 45 of any desirable type. The rectifier 45 may be connectedwith a field pole winding for providing auxiliary excitation thereof,being, for

example, disposed in connection with the seriesv field windings I 1 andI3, and the commutating field windings 2I and 23 of the generatorthrough a reversing switch 24, or possibly connected to an independentexcitation winding. The switch 24 may be of any desirable construction,for effecting a ready reversal of the direction of the excitationcurrent supplied to the'excitation winding, thereby reversing theterminal polarity of the generator at-the operator's will.

In accordance with the general construction of cross-field generators,it may be seen that magnetic shunt members 5I and I3 of the generatorIll may be provided with short-circuiting damper windings 54 and 55,respectively, and `disposed in connection with the shoe portion 21 05 ofthe field pole member I5-by meanssuch as bolt members 55 which passthrough the shunt members and are secured in threaded engagement withthe shoe portion 21. Springs 51, may

be positioned uponthe boit members 56 for rev 70 siliently biasing theshunt members 5I and 53,nto

engagement with the shoe portion 21, yet permitting their adjustmentrelative tol thev shoe portion 25 of the field pole member I3, by meansu of a threaded shaft 53, which is disposed' t0 engage extended portions59 and 53 of the shunt members 5I and 53, respectively.

Referring to Fig. 2, it may be seen that in an alternative form of myinvention, the shoe portions 53 and 65 of field pole members may be 5provided with arcuate surfaces adjacent to the armature I2 and parallelto the surface thereof, but comprising portions 81, 33 and 10, 1I,respectively, of different radii. Air gaps 13, 14 and 15, 36,respectively, which are parallel, but 10 of different lengths arethereby provided to eiTect an increase of air gap reluctance in thedirection of armature rotation, and cooperate with the increased eldwinding excitation to effect polarity control of a cross field generatorl5 without undue increase-of the no-load armature current.

For a complete understanding of the nature of my invention, it must berealizedthat yin a generator of the cross-field type, as shown in 20Fig. l, there will be a circulating current i flowing between theauxiliary brushes 35 when the generator is running without load.Inasmuch as this current is induced by the conductors on the armaturecutting the residual magnetic flux of -25 the field pole members I3 andI4, the path of which isindicated by the dotted line .p-I, it will beunderstood that in providing auxiliary polarity determining excitationfor a field pole winding, there would normally be an increase of the 30fluxv p-I due to the increased excitation, and, therefore, an increasedno-load circulating current in the armature. While auxiliary polaritycontrol excitation ofA a field pole winding has been found essential inorder to prevent ac'ci- 35 dental reversal, and permit ready reversal atwill of the terminal polarity of a generator of the cross-field type, ithas been found that the increase incurred thereby in the no-loadarmature circulating current has in many instances 9 been so great as toproduce excessive sparking of the auxiliary brushes 35 at-no-load andsubstantialiyreduce the stability of the generator under load. Byadapting shoe members4 25 ano 21 to provide air gaps 29 and 30,respectively, u which have increased reluctance from the leading' shoetip to the trailing tip, as indicated in the figures of the accompanyingdrawing, I have found that it is possible to provide auxiliaryexcitation of the eld pole windings of a generator u of the cross-fieldtype and thereby readily determine and control the terminal polarity ofthe generator,.yet not appreciably increase the noload circulatingcurrent of the armature. In this manner, excessive sparking at 4theaux'liary u brushes and wear of the commutator are prevented,"and thestability of the generator is markedly improved under load conditions.

Since certain changes may be made in the above construction, anddifferent embodiments 00 of the invention may be made without departingfrom the spirit thereof, it is intended that all matter contained in theabove description or shown in the accompanying drawing, shall be takenas descriptive, and not in a limiting sense. u;

I claim as my invention: i

l. The combination in a generator of the crossfield type, of an armaturehaving main and auxiliary brushes, circuit means connecting theauxiliary brushes to provide a closed armature 7.0

- circuit for producing a cross-field flux, field pole members havingfield windings positioned thereon, auxiliaryv polarity control meansincluding a source of excitation and switch means for selectivelyconnecting the source to at least one n y ber, and an arcuate pole shoemember. positioned 15 connecting the auxiliary brushes to provideanbetween each eld pole member and the arma- .ture having the surfaceportions adjacent the armature so positioned relative thereto as toprovide air gaps therebetween of varying reluctanceto prevent anyincrease in the no-load air gap flux without aiecting the value o!the-'crossneld flux.

2. The combination in a generator of the crossy field type having a pairoi-oppositely positioned ileld pole members provided with iieldwindings,

an 'armature rotatably positioned therebetween I having main andauxiliary brushes, circuit means armature circuit for producing across-ileld nux, of means including an independent source and reversibleswitch means for supplying an aux-V iliary polarity controllingpotential to at least one of the said iield windings for determiningLthe direction of the no-load magnetomotive force of the ileld polemembers, and varcuate shoe members associated with the eld pole membersto provide a low reluctance paththerethroughv for a cross-eld ilux thesurface portions of the shoe members adjacent the armature being sorelated thereto asto provideairl gaps therebe-` tween of increasingreluctance in the direction of armature rotation so as to prevent theauxiliary polarity controlling potential from increasing the no-load airgap iiux, without. altering he reluctance of the path oi.' thecross-'ileld 3. A generator "of the cross-ileld type comprising, a pairof ileld pole members having eld windings thereon, an armature havingmain and auxiliary brushes, circuit means connecting the auxiliarybrushes to provide an armature circuit for producing a cross-ileld ilux,meansvincluding an external source and a switch for selectivelyconnectingl the source to at least one of the ileld windings to controlthe no-loadA terminal polarity or the generator by controlling theno-load mag-' netomotive force'of the iield pole members, and arcuateshoe members disposed onthe ileld pole members tovprovide a lowreluctance path for the cross-held linx therethrough'having the surfaceportion thereof adjacent the armature positioned-relative thereto toprovide air gaps of' decreased reluctance at the leading tip andinlculating amature current.y

creased reluctance at the trailing tip so as. to substantiallyneutralize the eiiect oftheiincreased field pole magnetomotive force onthe no-load air gap ilux.

4. In a generator of the' cross-field type, the

combination, of a rotatable armature having .main and auxiliary brushes,circuit means connecting the auxiliary brushes' to provide an armaturecircuit for a cross magnetizing armature current, a ,plurality or neldpole members asso' 'ciated with the armature comprising main bodyportions and shoe portions disposed adiacent to the armature to providean air gap therebetween of increased reluctance in the direction oiarmature rotation, a plurality of field pole wind` .ings disposed onsaid field pole members and .connected in series circuit relation withthe main brushes, and means including a separate source land a switchfor providing for selective aux-` iliary excitation of at least one ofsaid iield pole windings to control the polarity of the no-load magneticiiux oi the body member of a neld pole member, the variation in air gapreluctance being disposed .to limit the no-load magnetic iluxof the`body member of the iield pole member to prevent an increase in theno-load cir.

' 5. The combination in a generator of the crossvileld type, of arotatable armature having main.

and auxiliary brushes, circuit means connecting .theauxiliary brushes, aplurality of eld pole members having main body portions and shoeportions adjacent to the/armature to provide y air gaps therebetween ofincreased reluctance at the trailing portion and decreased reluctance atthe leading portion of a pole shoe from the normal value of air gapreluctance, a plurality of windings associated with the eld polemembers, and means including a separate source and a reversible switchselectively applying an auxiliary polarity controlling potential to atleast one of said windings, the shoe portions of the field lpole membersbeing so shaped that thel variation in air gap reluctance between thearmature and a eld pole member is disposed. to substantially prevent anyeiIective increase in the no-load air gap ilux resulting from theapplication of the auxiliary polarity controllingpo'- tential to theileld wnmm R. naanmo.

